Always error on invalid macro fragment specifiers

src/libsyntax/ext/tt/macro_rules.rs

@@ -334,6 +334,10 @@ fn check_matcher<'a, I>(cx: &mut ExtCtxt, matcher: I, follow: &Token)
                 let tok = if let TtToken(_, ref tok) = *token { tok } else { unreachable!() };
                 // If T' is in the set FOLLOW(NT), continue. Else, reject.
                 match (&next_token, is_in_follow(cx, &next_token, frag_spec.as_str())) {
+                    (_, Err(msg)) => {
+                        cx.span_err(sp, &msg);
+                        continue
+                    }
                     (&Eof, _) => return Some((sp, tok.clone())),
                     (_, Ok(true)) => continue,
                     (next, Ok(false)) => {
@@ -343,10 +347,6 @@ fn check_matcher<'a, I>(cx: &mut ExtCtxt, matcher: I, follow: &Token)
                                                  token_to_string(next)));
                         continue
                     },
-                    (_, Err(msg)) => {
-                        cx.span_err(sp, &msg);
-                        continue
-                    }
                 }
             },
             TtSequence(sp, ref seq) => {

src/test/compile-fail/unused-macro-with-bad-frag-spec.rs

@@ -0,0 +1,17 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Issue #21370
+
+macro_rules! test {
+    ($wrong:t_ty) => () //~ ERROR invalid fragment specifier `t_ty`
+}
+
+fn main() { }

src/test/compile-fail/unused-macro-with-follow-violation.rs

@@ -0,0 +1,15 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+macro_rules! test {
+    ($e:expr +) => () //~ ERROR not allowed for `expr` fragments
+}
+
+fn main() { }